1. Field of the Invention
The invention relates to a seal for an electrical connector, which seal has at least one opening for the introduction of an electrical contact that is connected to a conductor. Furthermore, the invention relates to a method for manufacturing a seal and a use of this seal in an electrical connector.
2. Summary of Prior Art
For electrical connectors with electrical contacts it is often necessary to seal the contact-making area of the connectors with respect to the housing. Basically two different methods are specified for this. It is possible to seal each individual contact, or each individual conductor, with respect to the connector housing, or a family seal can be used. The application of a family seal has considerable advantages particularly if the connector has a very large number of contacts which are packed very tightly.
A disadvantage of family seals is that they can easily be damaged. Family seals are firstly introduced into the connector housing and are then penetrated by the individual contacts when the contacts are introduced into the connector housing. If the contacts do not have a very smooth surface without corners and edges, the problem arises of either the seal being cut into or even material from the seal being carried out when the contact is introduced through the seal into the connector housing. If it is necessary to replace a contact, and the latter is repeatedly moved through a seal in different directions, this can lead to substantial damage of the family seal and also to the contamination of the contact surface of the contacts with particles of the seal.
U.S. Pat. No. 4,875,870 discloses an electrical connector in which a layer of gel is used as family seal. The connector housing is of two-part design here and has a first part in which a layer of gel and the chambers for the contacts are located, and a second part which can assume two different positions in relation to the first part. In a second position, the second part presses onto the gel like a cap and, by this compression, causes the gel to have a sealing effect.
GB 2 101 420-A discloses an underwater electrical connector having contacts disposed in a grease chamber sealed with a resilient diaphragm. A rigid plate member having openings according to the contacts is mounted adjacent the diaphragm. The plate member protects the diaphragm against damage.
An object of the invention is to specify a seal for an electrical connector, that can be used as a family seal and leads to a good sealing effect. Furthermore, an object of the invention is to specify a method for manufacturing such a seal, and a use of such a seal.
The object is achieved with respect to the seal by means of a seal which has at least one opening or the introduction of an electrical contact that is connected to a conductor, the seal being formed by an insulating foam whose cells are filled with a grease.
With regard to the method for manufacturing a seal, the object is achieved by means of a method with the following method steps: the material for the foam and the grease are mixed, the mixture is then introduced in a mould, the mould is closed with a cover and then the expansion and the curing of the foam take place.
A further solution is specified by means of a method in which a mat in the form of a plate having openings and made of an open-cell foam is impregnated with a grease and then provided with a closed surface.
Furthermore, a use of such a seal is specified in an electrical connector which comprises a housing with at least one chamber for the electrical contact, and has a pressure plate with at least one through hole, the seal being provided between the housing and pressure plate.
Advantageous developments are specified for each main claim in the subclaims.
A seal according to the invention has at least one opening for the introduction of an electrical contact, connected to a conductor, into an electrical connector, that is to say actually an opening for leading through an electrical contact; the seal comprises an insulating foam whose cells are filled with a grease. This foam can be an open-cell or closed-cell foam which has a closed surface at its outer walls. In the case of an open-cell foam, this surface can be formed by a film. In the case of a closed-cell foam, a closed surface is already available. In addition, the foam can have in the region of the surface, at least in the region of the top and bottom surface and advantageously also around the openings, a layer in which the cells are very small. The cells are substantially smaller in this layer in comparison with the rest of the foam.
The described structure proves particularly advantageous if the seal is damaged when the opening is penetrated by an electrical contact. As a result, the outer surface of the seal is cut into and the cells of the foam are correspondingly cut into. These cells are however filled with the grease. Since the seal is used in an electrical connector which has a pressure plate which correspondingly exerts a pressure on the seal, the grease will, as a result of this pressure, flow out of the cells which have been cut into and will have a sealing effect at the damaged points of the actual seal. The grease also acts as a lubricant and reduces the insertion forces.
If the contacts used are configured in such a way that the seal is not damaged, then no grease will leave the seal if it has a closed surface.
The term grease is to be understood for example as a mineral or synthetic oil which contains a thickening agent. It is particularly advantageous to use a silicone-based compound as grease. The use of a synthetic hydrocarbon grease is also possible. The cone penetration of the grease should be between 150 and 500{fraction (1/10)} mm (measured after DIN 51580).
For the characterization of the term foam: it will be a mixture of the polymer material with a gas. In this context, the gas produces cells or pores whose diameter is between 0.1 mm and 1 mm. The term foam does not necessarily mean that it is manufactured by xe2x80x9cexpansionxe2x80x9d.
The insulating foam is for example a material with the following properties in the expanded state: tensile strength 0.03 MPa-0.9 MPa, elongation 40%-100%.
It is particularly advantageous to use, for example, a two-component silicone foam as closed-cell foam and a polyurethane foam as open-cell foam.
By using these materials, it is possible to manufacture a hybrid foam/grease system which has the properties necessary for the seal.
Owing to the particular features of the seal, it is suitable in particular for use as a family seal.
The seal can be manufactured in a plurality of ways. A first possibility is to proceed as follows: firstly, the material for the foam and the grease are mixed together. The mixture is then introduced into a mould which is closed with a cover. Then, the mixture is expanded and the foam is cured.
It is particularly advantageous that the mould already has pins by means of which the openings of the seal are manufactured. The openings are therefore not manufactured by the introduction of the contacts.
A particular advantage is also obtained if the mixture is introduced into a housing of an electrical connector in whose chambers there are pins which appropriately project into the opening into which the mixture is introduced. Then, a cover is fitted onto the housing, which cover is in contact with the pins so that a seal with openings is produced. Instead of the introduction into the housing, introduction of the mixture into a depression in the pressure plate is also possible, the through holes in the pressure plate being closed by pins.
Another possibility is the introduction of the mixture in to a mould, which is closed by the pressure plate. The pressure plate includes integrated pins instead of through openings for the contacts. The pressure plate further includes holes for the mixture to expand in. The mixture is then foamed and cured. The seal is integrated into the pressure plate. The pressure plate is cut so that pins are cut out by a punch and through openings are so created. The cut pins are removed from the pressure plate with the integrated seal.
Another possible manufacturing method is to manufacture a relatively large mat having through-holes in the foam filled with grease, from which mat seals of the appropriate size are cut out or punched out. If the mat comprises a closed-cell foam, closed surfaces are also produced at the interfaces. The grease of the cells which are cut into in the region of the interfaces will emerge from them but the sealing effect is not impaired by this.
A further possible manufacturing method for a seal according to the invention is to impregnate a mat having openings and made of an open-cell foam with a grease, and then to provide it with a closed surface, that is to say for example to coat it with a film.
In order to initiate the process of expansion and curing and to achieve uniform expansion, the mould or the housing with the mixture should be placed in an oven. The appropriate temperatures and the curing time are essentially dependent here on the materials used.
If the mixture has already been expanded in the housing of the electrical connector, all that is then necessary is to remove the cover which has been put on, to remove the pins from the chambers of the housing and then to close the housing again with a pressure plate which has corresponding through holes for the contacts. It is particularly advantageous here if the pressure plate has a first engagement and a final engagement position with respect to the housing. In the final engagement position, the seal is then compressed, while there is no such compression, or only a smaller compression, in the first engagement position. As a result, contacts can be easily introduced in the first engagement position and the good sealing can be achieved in the final engagement position. If the seal were to be damaged during the introduction of the contacts, that is to say the outer closed surface were to be damaged, this causes cells, which are filled with grease, to be cut into. The engagement of the pressure plate in the final engagement position will now exert a pressure on the seal. This means that the grease will emerge from the damaged cells and, as a result, a seal is formed around the conductor, which is connected to an electrical contact.
The main advantages of the foam and grease seal are:
1. An equal force distribution of the insertion force as the grease acts as a liquid. The force distribution is due to the xe2x80x9chydraulic effectxe2x80x9d of the grease.
2. The insertion forces are low as the grease acts as a lubricant ( less than 5N).
3. Small damages in the seal are recovered and the compression force necessary for a good sealing does not increase after several insertions of contact through the same opening.